1. Field of the Invention
The present invention relates to a pyrene derivative that emits light efficiently, has great heat resistance, permits an uniform film to be formed, and is morphologically stable, and further relates to a light-emitting element that has an anode, a cathode, and a layer including an organic compound from which luminescence can be obtained by applying an electric field (hereinafter, referred to as “a layer including a luminescent layer”).
2. Description of the Related Art
Organic compounds include more varied material kinds of materials in comparison with inorganic compounds, and have a possibility that a material that has various functions can be synthesized by an appropriate molecular design. Also, they have features that a molded article such as a film is flexible and excellent workability is provided by polymerization. Based on these advantages, photonics and electronics utilizing functional organic materials have been attracting attention recently.
For example, examples of a photoelectric device utilizing an organic semiconductor material as a functional organic material include a solar cell and a light-emitting device (also referred to as an organic electroluminescent device), which are devices utilizing an electric property (carrier transporting property) and an optical property (light absorption or light emission) of the organic semiconductor material, and, among them, the light-emitting device has been showing remarkable progresses.
The light-emitting device has a light-emitting element interposing a layer including a luminescent material between a pair of electrodes (an anode and a cathode), which is said to have the light emission mechanism that a hole injected from the anode and an electron injected from the cathode are recombined in the luminescence center of the layer including the luminescent material to form an excited molecule in an excited state when a voltage is applied between the both electrodes and energy is released to emit light while the excited molecule moves back toward the ground state. As the excited state, a singlet excited state and a triplet excited state are known, and luminescence is said to be possible through any of the singlet excited state and the triplet excited state.
In order to manufacture a full-color display by using the light-emitting element, it is necessary to arrange pixels that emit light of three primary colors of red, green, and blue. As a method for that purpose, there are various applicable methods. However, blue luminescence is indispensable in any method, and it is desired to provide a blue light-emitting element that is high in luminance, efficiency, and color purity.
Meanwhile, as a conventional blue light-emitting element, a light-emitting element using 1,3,6,8-tetraphenylpyrene or a derivative thereof as a luminescent material is known (refer to Patent Document 1 and Non-Patent Document1, for example). However, since a thin film of the luminescent material is likely to undergo crystallization, there is a problem that it is difficult to keep the film morphologically uniform and obtain stable light emission for a long stretch of time. Further, the luminous efficiency is insufficient.
(Patent Document 1)
Japanese Patent Laid-Open No. 2001-118682
(Non-Patent Document 1)
Wataru Sotoyama, et al., 2003 SID International Symposium Digest of Technical Papers, Vol. 34, 1294–1297 (2003)